Many automatic dishwashing compositions incorporate dispersant polymers with calcium ion-capturing ability. Many acrylic acid-based polymers having carboxyl groups, maleic acid/acrylic acid-based copolymers, and the like have been conventionally known to have a calcium ion-capturing ability, clay-dispersing ability, and the like, and hence have been widely used in detergent compositions, inorganic pigment dispersants, agglomerate reagents, scale inhibitors, chelating agents, fiber treatment agents, and the like.
As a method of producing the acrylic acid-based polymer, there are disclosed JP 62-270605 A, JP 05-239114 A, and the like. In addition, as a method of producing the maleic acid/acrylic acid-based copolymer, there are disclosed various documents such as JP 05-247143 A, JP 03-2167 B, JP 03-14046 B, and JP 2574144 B, and thus improvements of the above abilities have been attempted.
However, while having high calcium ion-capturing ability, the maleic acid/acrylic acid-based copolymer hardly exerts the effect of the clay-dispersing ability, in particular, under the condition where the water hardness is high. This is because, in particular the maleic acid-based polymer deteriorates remarkably in antigelation properties (hardness resistance, that is, water-solubility of the polymer in the presence of a hardness component) when a content of a structural unit originating from a maleic acid increases. There is not so large problem in the case of soft water having low hardness such as water in Japan, but worldwide, use of the copolymer causes a big problem in regions where water has high hardness, such as United States of America and China.
In addition, the acrylic acid-based polymer exerts the clay-dispersing ability to some degree due to the absence of a structural unit originating from a maleic acid, but it is difficult to say that the acrylic acid-based polymer has sufficient calcium ion-capturing ability.
The water-soluble copolymer, compared to the maleic acid/acrylic acid-based copolymer or the acrylic acid-based polymer, exerts favorable calcium ion-capturing ability, clay-dispersing ability, and a calcium carbonate deposition-suppressing ability under high hardness. However, the water-soluble copolymer has a problem that a detergent is colored yellow when used as a powdery additive for detergent.